The default colour themes installed with Xcode 4 are pretty drab, and leave much to be desired when it comes to legibility. They seem to have been designed by programmers. However, your code doesn't have to look so bleak.
Last week, I discovered Ethan Schoonover's Solarized colour scheme, which is a thoroughly well thought out and designed palette for use in text editors such as Vim, or as general terminal colours. He provided both light and dark themes, which are in a word, beautiful.
Somebody was quick to port the colours to an Xcode 4 theme, although just the Dark theme. Since the themes were available on GitHub, I decided to fork Varikin's project and add my own Light theme (Varikin did the hard work — the Light theme only differs by two colours). My changes have been accepted back in to the original Xcode fork.
Until Xcode 4, I'd been using a different theme, Humane, with minor modifications. But as the theme format changed with Xcode 4, I just defaulted to using the standard colour theme. After some digging around this week, I discovered a tool to upgrade Xcode 3 themes to the newer format. All three themes use Menlo 12 pt., although 11 pt. works well, too.
Comparing my modified Humane theme with the Solarize Light theme, I certainly prefer the latter. It's just better designed. However, I thought I'd share all three, and the conversion script, to anyone interested in making Xcode easier on the eyes.
I've grouped the themes together in a GitHub repository that you can browse at your leisure. The ReadMe also shows a preview image of what each of the three themes look like while editing Objective-C, so you can get an idea of how it might look with your code. Also included in the ReadMe are instructions for installing the themes.
If you make any modifications to the themes, please fork the project on GitHub and be sure to let me know if you make any improvements. If you have other themes you think are worthy of this collection, let me know as well.